Plug and abandonment operations at Njord

Abstract

Since more and more of the wells in the North Sea are meeting their end of lifetime, plug and abandonment is of great present interest. When a well reaches its end of production, the well can be permanently abandoned, or the slot and upper part of the well can be re-used to drill towards another target. This can be done by making a sidetrack from the original wellbore.

Plug and abandonment operations may be problematic and therefore time consuming. Extra time consumption results in a lot of extra costs, and budgets are exceeded. In addition, plug and abandonment operations may cause well control situations, which is a safety and envi-ronmental risk.

The main intention with this project was to highlight and find the operations during plug and abandonment of wells that have caused most downtime and well control issues. The most problematic situations needed to be found and evaluated, and a proposal for improvements should be given.

The study showed that retrieval of casing and section milling was the most challenging opera-tions during plug and abandonment (P&A). Cutting and pulling of casing and completion is time consuming, and represents an uncertainty regarding well control. Section milling results in a lot of steel swarf in the well and deposits inside equipment like the BOP.

When the annulus behind casings are logged, there is limited time to interpret logs if an effec-tive operation shall be maintained. The poor quality of the logs makes the interpretation job even harder, especially logging of annulus with several layers of casings in the cross section.

Through present investigation a need of improved logging has been revealed, and thus avoid stuck casing by having a clear indication of what components are present in the annulus. Pre-ventive measures are to clean the well properly during the drilling operation to avoid a lot of cuttings in the well, and to log the casing annulus after cementing. Another idea is to displace the annulus behind casings to brine to avoid settling of barite. For milling operations, the well should be cleaned properly if there is any suspicion that swarf in the well could cause prob-lems for later operations. Alternatively, new methods could be used to leave swarf downhole in the well. The SwarfPak that is discussed later in this report is one such development.